FOLIA HORTICULTURAE Folia Hort. 23/2 (2011): 125-129 Published by the Polish Society DOI: 10.2478/v10245-011-0019-0 for Horticultural Science since 1989 In vitro flowering of Petunia × atkinsiana D. Don Danuta Kulpa, Natalia Nowak Department of Horiculture Plant Breeding West-Pomeranien University of Technology Janosika 8, 71-424 Szczecin, Poland e-mail: [email protected] ABSTRACT The aim of this study was an attempt to determine the influence of PGRs – auxins, cytokinins and gibberellic acid – on the flowering and morphogenesis of ‘Flash Red’ Petunia × atkinsiana D. Don in vitro. The best -3 results at the propagation stage were obtained on an MS medium supplemented with 0.5 mg dm GA3. The petunia plants propagated under these conditions developed high main shoots and a large number of leaves and adventitious shoots. The plants with the best-developed root system were regenerated on an MS medium supplemented with 0.5 and 1.0 mg dm-3 IAA. Flowering initiation should be performed using an MS medium supplemented with 0.5 mg dm-3 KIN. Key words: micropropagation, morphogenesis, plant growth regulators INTRODUCTION jessamine (Jumin and Ahmad 1999), orchids (Tee et al. 2008), bamboo (Lin et al. 2003, 2007, Nadgauda Petunia × atkinsiana D. Don is a hybrid derived et al. 1997, Ramanayake et al. 2001), gentian from two endemic species of South America, (Zhang and Leung 2002), Dioscorea zingiberensis Petunia integrifolia and Petunia axillaris. This (Huang et al. 2009) and date palm (Masmoudi- species has been grown all over the world in Allouche et al. 2010). Developing the methods of gardens and on balconies (Stehmann et al. 2009). At inducing petunia flowering in vitro would facilitate present, many varieties of this plant are available, the fast selection of plants with a desired phenotype varying in resistance to drought and diseases, soil for plant breeders. This system would be very requirements, conformation, flower size and colour. useful for researchers studying flower development. Due to its great popularity among consumers, Flowering plantlets in vitro have good commercial breeding works are being conducted in order to potential as ornamentals as well. develop new interesting varieties and propagate Plant flowering is controlled by many factors, them on a large scale (Tsuda et al 2004). both genetic and environmental. The most important In recent years, there has been a great interest factors include: medium pH (Nadgauda et al. 1997), among breeders in biotechnological methods the content of sucrose (Lin et al. 2003, Aneesh et al. including in vitro culture, which can accelerate 2007) or agar in the medium (Kachonpadungkitti and intensify the breeding process. They are used, et al. 2001), light intensity and even the size of first of all, in order to obtain a large population of explants (Taylor et al. 2005). However, the most progeny genetically identical with the maternal important of these is the content of plant growth plants in a short amount of time. Several reports regulators added to media in vitro (Levy and Dean indicate sporadic flowering and seed setting 1998, Taylor and van Staden 2006). However, the under these conditions in: roses (Wang et al. application of phytohormones is not easy, as their 2002), Spathiphyllum (Dewir et. al. 2007), orange effects depend on their concentration, in vitro 126 Flowering of Petunia in vitro cultures conditions, and plant species. Therefore, in each of roots and number of formed flower buds were case the kind and concentration of applied growth determined. The significance of differences was regulators must be chosen experimentally. verified using analysis of variance and the Tukey Hence, the aim of this research was to determine test at α = 0.05. Homogenous groups between the the influence of the concentration of auxins, examined combinations were labelled in the table cytokinins and gibberellic acid in the medium with successive letters of the alphabet. on petunia (‘Flash Red’ Petunia × atkinsiana D. Don) propagated in vitro and also the choice of the RESULTS AND DISCUSSION optimal media for propagation and rooting as well The studies conducted show that the addition of as the induction of floweringin vitro. plant growth regulators to the media has a highly significant influence on petunia morphogenesis and MATERIAL AND METHODS flowering. The development of the aboveground part ‘Flash Red’ Petunia × atkinsiana D. Don grown was particularly strongly stimulated by 0.5 mg dm-3 on an MS medium (Murashige and Skoog 1962) of gibberellic acid (Tab. 1). Plants from the media -3 without growth regulators was the plant material. with 0.5 mg dm GA3 produced the longest main Explants for the experiment consisting of one-node shoots (70.97 mm). Petunias regenerated on that shoot fragments, ca 1-cm long, were placed on the medium were characterised by the largest number MS medium supplemented with 0.5 and 1.0 mg of leaves (30.26), which is in agreement with the dm-3 KIN (kinetin), BAP (6-benzylaminopurine), findings of Farhatullah et al. (2007) in the studies IAA (indole-3-acetic acid) and GA3 (gibberellic on the effects of growth regulator on explants of acid). Plants on an MS medium without growth potato (‘Desiree’ Solanum tuberosum), which like regulators were the control group, and 100 explants petunia belongs to the family Solanaceae. In this were placed on each medium. case, 1.0 mg dm-3 of gibberellic acid significantly After adding growth regulators into the media, affected the development of foliage in comparison their pH was adjusted to 5.7 using 0.1 M solution with the control group. of HCl and NaOH. The media were supplemented IAA was found to be the strongest growth with 7 g dm-3 agar and 30 g dm-3 sucrose and heated regulator inducing rhizogenesis, irrespective of to cause agar polymerization; 300-ml jars filled the applied concentration. Petunias propagated with 30 ml of medium were autoclaved at 121°C on the media with IAA formed about 40% more for 20 minutes. roots than the control plants (on average 5.54 and Next, the cultures were kept in a growth 5.17 roots). The root length of petunias rooted on chamber at a temperature of 25°C, with daylight the media supplemented with IAA was close to at a 16-h photoperiod. Four weeks later, biometric those regenerated on the MS medium. A similar measurements were taken and the length of the main relationship was observed in the studies by shoot (mm), number of axillary shoots, plant weight Witomska and Ładożyńska (2001) on petunia of (g), number of leaves, root length (mm), number the group Ursynia, in which the addition of 1.0 mg Table 1. The influences of growth regulators on shoot and root formation ofPetunia × atkinsiana D. Don. Plant Length of Concentration Number of Number of Fresh weight Number of Length of root growth main shoot (mg dm-3) axillary shoots leaves (g) roots (mm) regulators (mm) 0.5 58.07 abc* 1.95 bcd 19.90 b 1.27 b 1.23 e 24.39 abc BAP 1.0 63.29 abc 2.73 bc 21.01 b 1.42 b 3.40 bcd 47.88 a 0.5 70.97 a 4.09 a 30.26 a 1.59 ab 1.56 cde 8.89 bc GA 3 1.0 52.72 bc 4.71 a 32.03 a 1.26 b 0.36 e 2.51 c 0.5 66.12 ab 2.88 b 21.67 b 2.06 a 5.54 a 40.51 a IAA 1.0 59.03 abc 1.54 cd 17.12 b 1.66 ab 5.17 ab 44.21 a 0.5 71.35 a 1.99 bcd 20.06 b 1.44 b 3.64 abc 30.74 ab KIN 1.0 65.90 ab 2.46 bcd 28.20 a 1.28 b 1.52 de 25.20 abc MS - Control 46.65 c 1.74 cd 17.87 b 1.27 b 3.77 ab 43.35 a LSD 0.05 17.67 1.03 4.88 0.52 2.08 23.52 *Values designated with the same letters within columns do not significantly differ at α = 0.05 Danuta Kulpa, Natalia Nowak 127 3 2,5 2.39 2 1.76 1.43 1,5 1.31 1.30 1 0.78 0.77 0.83 0.44 0,5 Number of flowers per plant 0 Control IAA 0.5 IAA 1.0 BAP 0.5 BAP 1.0 KIN 0.5 KIN 1.0 GA3 0.5 GA3 1.0 GA3 Plant growth regulator (mg dm-3) Figure 1. Number of flowers per petunia plant propagated on media with different plant growth regulators 90 82 80 70 62 60 54 56 50 43 40 30 32 30 24 25 % of of % flowering plants 20 10 0 Control IAA 0.5 IAA 1.0 IAA BAP 0.5 BAP 1.0 KIN 0.5 KIN 1.0 GA3 GA3 0.5 1.0 GA3 Plant growth regulator (mg dm-3) Figure 2. Percentage of flowering petunias propagated on media with different plant growth regulators dm-3 IAA resulted in over three times as many roots and zeatin positively affected the development of as in the control trial and their length was over 20% inflorescence. Studying the effect of cytokinin on higher than the roots of petunias regenerated on the the development of Dioscorea zingiberensis in medium without growth regulators. the in vitro culture, Huang at al. (2009) observed Gibberellic acid and cytokinins (especially a beneficial effect of BAP at the concentration 1.0 BAP and TDZ) are considered growth regulators to 4.0 mg dm-3 on inducing flowering.